Perhaps this one: https://github.com/mit-pdos/xv6-riscv ?
The old xv6 is x86-based and it's not officialy maintained anymore.
Or Xinu: https://xinu.cs.purdue.edu. There's a BeagleBone (ARM) port.
The old xv6 is x86-based and it's not officialy maintained anymore.
Or Xinu: https://xinu.cs.purdue.edu. There's a BeagleBone (ARM) port.
If you really did want to work with an existing OS for actual research/experimentation purposes, and you're a fan of C, I would go with Plan 9/9front. There's a reason Bell Labs ditched Unix--because it wasn't a worthy research platform anymore.
For something non-X86, try digging at: http://wiki.osdev.org/Projects Perhaps you can find something suits your preference.
Which is sensible. There's way too much legacy crap and ugliness that needs to be dealt with in that ISA to distract from the purpose of the project, which is to teach OS development.